HADOOP-8710 | Major | Remove ability for users to easily run the trash emptier

The trash emptier may no longer be run using “hadoop org.apache.hadoop.fs.Trash”. The trash emptier runs on the NameNode (if configured). Old trash checkpoints may be deleted using “hadoop fs -expunge”.

This is an incompatible change: Before this change, if a file is already open for write by one client, and another client calls fs.create() with overwrite=true, an AlreadyBeingCreatedException is thrown. After this change, the file will be deleted and the new file will be created successfully.

The datanode now performs 4MB readahead by default when reading data from its disks, if the native libraries are present. This has been shown to improve performance in many workloads. The feature may be disabled by setting dfs.datanode.readahead.bytes to “0”.

{{dfs.namenode.replication.work.multiplier.per.iteration}} for controlling replication rate. This in turn allows controlling the time it takes for decommissioning.

HDFS no longer silently ignores missing or unreadable host files specified by dfs.hosts or dfs.hosts.exclude. In order to specify that no hosts should be included or excluded, administrators should either refrain from setting the relevant config properties, or create an empty file in order to represent an empty list.

Due to the requirement that KSSL use weak encryption types for Kerberos tickets, HTTP authentication to the NameNode will now use SPNEGO by default. This will require users of previous branch-1 releases with security enabled to modify their configurations and create new Kerberos principals in order to use SPNEGO. The old behavior of using KSSL can optionally be enabled by setting the configuration option “hadoop.security.use-weak-http-crypto” to “true”.